This invention relates to a flux gate type magnetic sensor adapted for the measurement of a very weak magnetic field such as geomagnetism. In particular, this invention relates to a biaxial flux gate type magnetic sensor capable of detecting magnetic fields in two axial directions by means of one thin-film sensor and suited to be used as a direction sensor such as for navigation.
As shown schematically in FIG. 6, a flux gate type magnetic sensor generally includes a core 11 of a magnetic material around which one excitation coil 12 and two detection coils 13a and 13b are wound, the two detection coils 13a and 13b being wound in mutually opposite directions in so-called differential connection, connected at one end of each. As an AC current is caused to flow through the excitation coil 12 as an excitation current, the AC magnetic flux generated thereby along the core 11 penetrates the detection coils 13a and 13b in different directions. If the sensor under this condition is subjected to an external magnetic field, the magnetic flux due to this field acts in the same direction on the two detection coils 13a and 13b, and this means that the magnetic fluxes through them may be interpreted as being biased in mutually opposite directions by this external magnetic field. Thus, it is possible to take out of the ends of the two detection coils an AC voltage signal which is proportional to the external field and has a frequency twice that of the excitation current. If this AC voltage signal is detected, say, after amplified by an AC amplifier and then rectified, it can serve as a magnetic sensor with good sensitivity and stable against temperature variations.
FIG. 6 shows a core 11 in the shape of a bar and the sensor is sometimes referred to as a solenoid type. FIG. 7 shows a sensor of a so-called ring core type, having a core 21 in the shape of a ring. For the sake of simplicity, FIG. 7 does not show the excitation coil for the sensor but it is actually wound uniformly around the entirety of the core 21 so as to spiral alternately with the helix of each of the detector coils 23a and 23b. 
In addition to the above, Japanese Patent Publication Tokkai 7-191118 has disclosed a so-called thin-film flux gate type magnetic sensor, as a kind of flux gate type magnetic sensor of the ring core type, having its ring core, excitation coil and detection coils formed with a thin film by the semiconductor production technology such that the sensor element can be miniaturized and the detection characteristics can be improved.
With each of the flux gate type magnetic sensors described above, the flux of the magnetic field to be detected must pass through the detection coil. Thus, each of these sensor has a so-called sensitivity axis (as indicated by arrow S in FIGS. 6 and 7). If a direction sensor, say, for detecting geomagnetism, is desired, therefore, two of these flux gate type magnetic sensors must be set such that their sensitivity axes are perpendicular to each other and that signals are individually taken out of them for detecting magnetism in two axial directions. A method of this kind introduces errors caused by the mechanical positioning of the sensors. The error is even magnified when the direction of the magnetic field is calculated on the basis of the detected signals
It is therefore an object of this invention to provide a biaxial flux gate type magnetic sensor which is not only capable of detecting magnetism independently in two axial directions by means of a single element so as to be able to serve as a direction sensor having no angular errors but also advantageous from the point of cost, requiring only a small space.
A biaxial flux gate type magnetic sensor embodying this invention, with which the above and other objects can be accomplished, may be characterized not only as having a core comprising a magnetic thin film in the shape of a loop, patterned upper and lower electrically conductive thin-film layers respectively above and below this thin-film core each with an insulating layer in between, and electrically conductive connecting members each extending between and electrically connecting these upper and lower electrically conductive layers but also wherein these upper and lower electrically conductive layers are patterned and the connecting members connect them such that they together provide an excitation coil and four detection coils. These coils are each formed so as to be wound helically, uniformly and alternately after each turn around and along a circumferential direction of the loop-shaped core by passing both inside and outside the loop. The loop is of a shape which is symmetrical with respect to two mutually perpendicular directions and is divided into four mutually symmetric sections and each of the four detection coils is wound along and around a different one of the four sections. Each mutually oppositely situated pair of detection coils on the core is wound in mutually opposite directions and connected to each other.